import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // TRY THIS: Try running your application with "flutter run". You'll see
        // the application has a purple toolbar. Then, without quitting the app,
        // try changing the seedColor in the colorScheme below to Colors.green
        // and then invoke "hot reload" (save your changes or press the "hot
        // reload" button in a Flutter-supported IDE, or press "r" if you used
        // the command line to start the app).
        //
        // Notice that the counter didn't reset back to zero; the application
        // state is not lost during the reload. To reset the state, use hot
        // restart instead.
        //
        // This works for code too, not just values: Most code changes can be
        // tested with just a hot reload.
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text('UTC vs Local Time Example'),
            const SizedBox(height: 20),
            ElevatedButton(
              onPressed: () {
                _showDateTimeExample(context);
              },
              child: const Text('Show Example'),
            ),
          ],
        ),
      ),
    );
  }

  void _showDateTimeExample(BuildContext context) {
    // Example dates around DST transition
    final localDate1 = DateTime(2023, 3, 11); // Before DST starts
    final localDate2 = DateTime(2023, 3, 12); // After DST starts

    final utcDate1 = DateTime.utc(2023, 3, 11);
    final utcDate2 = DateTime.utc(2023, 3, 12);

    final differenceLocal = localDate2.difference(localDate1).inDays;
    final differenceUTC = utcDate2.difference(utcDate1).inDays;

    showDialog(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: const Text('UTC vs Local Time Calculation'),
          content: SingleChildScrollView(
            child: Column(
              mainAxisSize: MainAxisSize.min,
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                const Text('Local Time Calculation:'),
                Text('Date1: $localDate1'),
                Text('Date2: $localDate2'),
                Text(
                  'Difference: $differenceLocal days (may be incorrect due to DST)',
                ),
                const SizedBox(height: 20),
                const Text('UTC Time Calculation:'),
                Text('Date1: $utcDate1'),
                Text('Date2: $utcDate2'),
                Text('Difference: $differenceUTC days (always correct)'),
                const SizedBox(height: 20),
                const Text('Conclusion:'),
                const Text(
                  'Using UTC ensures consistent day calculations regardless of DST changes.',
                ),
              ],
            ),
          ),
          actions: [
            TextButton(
              onPressed: () => Navigator.pop(context),
              child: const Text('OK'),
            ),
          ],
        );
      },
    );
  }
}
